The present invention relates to the field of dry strength additives for paper products. More specifically, the present invention is a water-soluble graft copolymer of cationic starch, nonionic vinyl monomers, and cationic monomers.
Water-soluble polyacrylamides are used at present to provide dry strength to paper. They are added to pulp as wet-end additives, and are relatively effective in increasing the dry tensile strength of the resulting paper. However, polyacrylamides are derived from petroleum products, and their cost therefore is linked to the fluctuating price of crude oil. In addition, petroleum is a nonrenewable natural resource, the supply of which is finite. Therefore, there is a continuing need in the paper making field for a cheaper stably priced alternative to polyacrylamide, which is water soluble, which can perform more efficiently, and which can be made from annually renewable natural sources.